Inflammatory bowel disease (IBD), which occurs world-wide and afflicts millions of people, is the collective term used to describe three gastrointestinal disorders of unknown etiology: Crohn's disease (CD), ulcerative colitis (UC), and indeterminate colitis (IC). IBD, together with irritable bowel syndrome (IBS), will affect one-half of all Americans during their lifetime, at a cost of greater than $2.6 billion dollars for IBD and greater than $8 billion dollars for IBS. A primary determinant of these high medical costs is the difficulty of diagnosing digestive diseases. The cost of IBD and IBS is compounded by lost productivity, with people suffering from these disorders missing at least 8 more days of work annually than the national average.
Inflammatory bowel disease has many symptoms in common with irritable bowel syndrome, including abdominal pain, chronic diarrhea, weight loss, and cramping, making definitive diagnosis extremely difficult. Of the 5 million people suspected of suffering from IBD in the United States, only 1 million are diagnosed as having IBD. The difficulty in differentially diagnosing IBD and IBS hampers early and effective treatment of these diseases. Thus, there is a need for rapid and sensitive testing methods for definitively distinguishing IBD from IBS.
Although progress has been made in precisely diagnosing clinical subtypes of IBD, current methods for diagnosing an individual as having either Crohn's disease, ulcerative colitis, or indeterminate colitis are relatively costly and require labor-intensive clinical, radiographic, endoscopic, and/or histological techniques. These costly techniques may be justified for those individuals previously diagnosed with or strongly suggested to have IBD, but a less expensive and highly sensitive alternative would be advantageous for first determining if an individual even has IBD. Such a highly sensitive primary screening assay would provide physicians with an inexpensive means for rapidly distinguishing individuals with IBD from those having IBS, thereby facilitating earlier and more appropriate therapeutic intervention and minimizing uncertainty for patients and their families. The primary screening assay could then be combined with a subsequent, highly specific assay for determining if an individual diagnosed with IBD has either Crohn's disease, ulcerative colitis, or indeterminate colitis.
Unfortunately, highly sensitive and inexpensive screening assays for distinguishing IBD from other digestive diseases presenting with similar symptoms and for differentiating between clinical subtypes of IBD are currently not available. Thus, there is a need for improved methods of diagnosing IBD at a very early stage of disease progression and for stratifying IBD into a clinical subtype such as Crohn's disease, ulcerative colitis, or indeterminate colitis. The present invention satisfies these needs and provides related advantages as well.